The embodiments herein relate to oil-in-water stable, emulsified spacer fluids for use in subterranean operations.
Subterranean operations (e.g., stimulation operations, sand control operations, completion operations, etc.) often involve placing a cement column around a casing (or liner) string in a wellbore. The cement column is formed by pumping a cement slurry through the bottom of the casing and out through an annulus between the outer casing wall and the formation face of the wellbore. The cement slurry develops into a gel and then cures in the annular space, thereby forming a column of hardened cement that, inter alia, supports and positions the casing in the wellbore and bonds the exterior surface of the casing to the subterranean formation. Among other things, the cement column may keep fresh water zones from becoming contaminated with produced fluids from within the wellbore. The cement column may also prevent unstable formations from caving in, thereby reducing the chance of a stuck drill pipe or a casing collapse. Additionally, the cement column forms a solid barrier to prevent fluid loss or contamination of production zones. The degree of success of subterranean operation involving placement of a cement column depends, therefore, at least in part, upon the successful cementing of the wellbore casing.
In order to effectively cement wellbore casing, adequate displacement of treatment fluids previously introduced into the wellbore (collectively referred to herein as “pre-cement treatment fluids”), particularly those comprising natural or synthetic oils (e.g., drilling fluids), is essential. This is because many pre-cement treatment fluids, particularly oleaginous fluids, tend to be incompatible with the cement curing processes. For this reason, adequate displacement of pre-cement treatment fluids is essential to achieve strong bonding between the cement and the subterranean formation and the cement and the casing (i.e., in the annulus between the outer casing wall and the formation face), to realize proper zonal isolation, structural integrity of the cement column, and the like. Traditionally, optimal removal of pre-cement treatment fluids prior to a cementing operation employs the use of spacer fluids formulated to have specific properties (e.g., plastic viscosity, yield point, density, and the like) depending on downhole requirements. As used herein, the term “spacer fluid” and all of its variants (e.g., “spacer”) refers to any fluid used to physically separate one fluid from another.
Generally, surfactant additives are included in spacer fluids as cleaning agents to both aid in displacing the pre-cement treatment fluids and to water-wet the face of the subterranean formation and/or the casing. As used herein, the term “water-wet” refers to disposition of a film of aqueous fluid (e.g., water) coating on a surface (e.g., the face of a subterranean formation or the surface of casing). Surfactants alone may poorly emulsify and/or excessively foam, thereby decreasing the effectiveness of the surfactant to remove a pre-cement treatment fluid. Surfactants may additionally remain in the subterranean formation where they contaminate the cement in cementing operations, often interfering with the mechanical properties of the cement and, thus, a cement column's integrity. That is, while surfactants are useful in removing pre-cement treatment fluids and in preparing the surfaces, they may be detrimental to the cement if left behind, particularly in large quantities.